1. Field of the Invention
The present invention relates to a process for preparing a light transmissive electromagnetic wave shielding material which is useful in an adhesive sheet used for a front filter of a plasma display panel (PDP) or windows of a building such as a hospital requiring electromagnetic wave shielding. In addition, the invention relates to an electromagnetic wave shielding material prepared by the above process and a display panel provided with the material.
2. Description of the Related Art
In recent years, along with the popularization of office automation equipments and communication equipments, there is fear that an electromagnetic wave generated by the equipments has an affect on the human body. In addition, the electromagnetic wave generated by a cell-phone may cause a precision equipment to malfunction. Therefore, the occurrence of the electromagnetic wave is of a problem to be solved.
For the reason, a light transmissive electromagnetic wave shielding material having a light transmissive property and an electromagnetic wave shielding property have been developed as a front filter of a plasma display panel and are put to practical use. Also the light transmissive electromagnetic wave shielding material is used as a window filter of a hospital and a laboratory where the precision equipment is installed in order to protect the precision equipment from the electromagnetic wave.
The light transmissive electromagnetic wave shielding material is required to balance the light transmissive property with the electromagnetic wave shielding property. Therefore, as the light transmissive electromagnetic wave shielding material, for example (1) a conductive layer having a fine mesh structure which is obtained by netting a metal wire or a conductive fabric is adopted. The mesh part of the conductive layer shields the electromagnetic wave and its opening part ensures the light transmissive property.
In addition, a variety of the light transmissive electromagnetic wave shielding materials is proposed as a filter for a electronic display. Other examples of the light transmissive electromagnetic wave shielding materials generally include (2) a transparent substrate on which a transparent conductive layer comprising metallic silver is formed, (3) a transparent substrate on which a copper layer having a mesh pattern is formed by etching, and (4) a transparent substrate on which a conductive ink comprising conductive powders is printed in the mesh pattern.
In order to balance the light transmissive property with the electromagnetic wave shielding property in the electromagnetic wave shielding layer, it is necessary to use the transparent conductive layer having a microscopic mesh pattern and an extremely narrow line width. However, it was difficult for the conventional light transmissive electromagnetic wave shielding material to balance the light transmissive property with the electromagnetic wave shielding property. This is, it is difficult for the light transmissive electromagnetic wave shielding material (1) to have the microscopic mesh pattern due to limitation for minimizing the line and distortion of line arrangement. The light transmissive electromagnetic wave shielding material (2) has problems that the electromagnetic wave shielding property is not enough and the metallic luster is too high. The light transmissive electromagnetic wave shielding material (3) has problems that the production process is long, the cost is high, and the light transmissive property is reduced by an adhesive layer arranged between the transparent substrate and the copper layer. In addition, the light transmissive electromagnetic wave shielding material (4) has problems that the electromagnetic wave shielding property is low. If the electromagnetic wave shielding property of the material (4) is increased by thickening the conductive ink layer, the light transmissive property may be reduced.
However, the light transmissive electromagnetic wave shielding material (4) is prepared by printing the conductive ink comprising a resin and a conductive powder such as metallic powder and carbon powder on the transparent substrate by offset printing using engraved plate to provide a printed pattern. Therefore, the process for preparing the light transmissive electromagnetic wave shielding material (4) does not need etching, and is easy and low in cost.
Documents 1 to 6 disclose a process for preparing a light transmissive electromagnetic wave shielding material, wherein the (4) is improved, which comprise;
printing the conductive ink on the transparent substrate in a specific pattern by offset printing using engraved plate to provide a printed pattern layer, and
forming a metallic layer on the printed pattern layer by electroless plating or electrolytic plating to enhancing the electromagnetic wave shielding property.
In addition, Document 7 discloses a process for preparing a light transmissive electromagnetic wave shielding material which comprise;
printing a paste comprising particles (supports) having a surface charge opposite to a noble-metal ultrafine particle catalyst and the precious-metals ultrafine particle catalyst formed on the particles in a specific pattern on a transparent substrate, and,
forming a metallic layer on the printed part by electroless plating.    Document 1: JP3017987-B    Document 2: JP3017988-B    Document 3: JP3241348-B    Document 4: JP3425400-B    Document 5: JP3544498-B    Document 6: JP3532146-B    Document 7: JP3363083-B